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Aug 30, 2018, 07:07 PM
jackerbes's Avatar
That is an interesting study and comparison. I don't pretend to be an aeronautics expert or even really understand all of what is said there. But the primary things that are compared are the lift and drag coefficients between a NACA 4415 airfoil and the same airfoil with a step added to the bottom at 55% of the chord (that compares well to the 50% we would normally use).

The KF version of the wing still had the same cross section shape as the NACA 4415 with curved surfaces on the top and bottom so it was not quite the same as the flat plate wings we most often build.

The NACA 4415 airfoil is much like the Clarke-Y airfoil other than it not being flat bottomed, it is more symmetrical and alike on both top and bottom.

But we could (and some have I'm sure) make our wing more closely match the test foil were willing to expend the extra time and work...

The comparison data was taken across a range of angles of attack that would be realistic for typical flights.

If you look at the graphs in the study, the wing with the KF step had more lift and it also had more drag. And it looked liked the amount of the lift increase (if the increase was expressed as a percentage) was fairly significant while the increase in drag was a much smaller percentage.

So, as we have pretty much learned, for a small increase in power the KF wing can easily match and even exceed the performance of conventional foils.

And I'll admit that the one area where the KF wing has a small performance penalty is that of the wings cross country speed in a power off glide. So it won't match up to high performance glider airfoils.

But, other than for competitive glider flying venues, it is still a great wing for use on gliders that are intended as glider flying trainers or to introduce the flier to process of glider flying.

It would be a wonderful thing to get these scientists to do comparison to some of the KFm variants as the KFm1, while a good wing, has been out performed by some of the other variants. And it would be interested to know how adding more steps or moving steps from the bottom to the top or both top and bottom changes the numbers.

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Sep 22, 2018, 01:04 PM
Registered User
Dickeroo's Avatar

Placement of a cylinder in the step cavity.

An interesting concept.

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